Optical transmission may be used as a means for communication between separate integrated circuit chips (inter-chip connections) and within components on the same chip (intra-chip connections). In chip-to-chip communication via optical interconnects, each chip on the circuit board is interfaced with a transmitter-receiver optoelectronic chip, and the two optoelectronic chips are connected via a planar dielectric waveguide or optic fiber. Likewise, optical waveguides may be used to connect components within a chip, such as between an integrated optical source and a detector. An integrated optical waveguide is an optical path formed on or within a dielectric substrate, e.g., oxide coated silicon substrate, using lithographic processing. The waveguide can be made of an inorganic crystal or semiconductor material having a higher index of refraction than the chip substrate to guide optical signals along the waveguide.
The coupling of a single-mode fiber to an integrated optical waveguide (and vice versa) is one of the most expensive and time-consuming manufacturing processes in the packaging of semiconductor photonics. Various solutions to the coupling problem have been proposed including using a lateral inverted taper structure or a vertical diffractive grating structure.
Another challenge is to hermetically seal the fibers or wires connected to the photonic-integrated chip because the performance of photonic elements may be adversely affected by environmental conditions such as moisture and contaminants. Therefore, environmental isolation of the photonic elements in the chip is a design challenge. FIG. 1A shows a conventional photonic integrated chip package 100 connected to an optical fiber 110 through a feedthrough 120. Feedthrough 120 provides a hermetic seal between the fiber 110 and the chip package 100. FIG. 1B shows a cross-section diagram of the hermetic fiber feedthrough 120. The feedthrough 120 encases an end stripped portion 130 of the optical fiber 110. The end stripped portion 130 of the optical fiber 110 is surrounded by a glass solder 140 material, such as lead borate glass. The glass solder 140 is stacked between a glass sleeve 150 and the fiber 110 thereby forming a bond between the fiber 110 and the glass sleeve 150 that is largely free from porosity. The glass sleeve 150 is encased by a glass solder 160 material, such as, lead borate glass, which in turn is surrounded by a outer sleeve 170. The outer sleeve 170 is made from metal, metallic alloy, ceramic, or glass. The end face 180 of the hermetically sealed fiber 110 is coupled to the photonic integrated chip package 100.
The conventional method described above however is costly and does not support high volume manufacturing. There is a need for an improved method to hermetically seal an optical fiber to a photonic-integrated chip. The method needs to be low cost and provide for a hermetically sealed connection with high reliability under extreme ambient conditions. In addition, the method needs to support high volume manufacturing processes and low processing temperatures.